Like many Chinese andrologists — doctors who specialize in medical conditions specific to men — I have a lot of patients asking me about male fertility. While most of them are couples hoping to get pregnant, some have a different request in mind: illegal sex screening.

Many such couples first claim to have trouble conceiving and inquire about in vitro fertilization (IVF). When I explain the mechanics of IVF to them, they ask if they can use the technology to ensure that they have a boy. Whenever this happens, I always point to one of the huge green-and-red signs that festoon the walls throughout the consultation rooms on my ward: “It is forbidden to determine the sex of a fetus for nonmedical reasons.”

But for some patients, this isn’t enough. One half of the couple — usually the man — will lower his voice and ask if sex screening is possible from a technological perspective. When I reply that yes, it is possible, but it is only permissible when at least one of the parents is carrying a hereditary disease, he will clear his throat and cut me off. “Money’s no object, if you catch my drift,” he’ll murmur. “Can you just help us have a boy?”

Of course, I refuse, and thus ends our consultation.

Our hospital delivers more babies than any other in the country, which perhaps makes us a natural target for such unscrupulous patients. Some of my world-wearier colleagues in the obstetrics department sometimes remark, “If you fertility doctors could just help them choose their child’s sex, we could save some women the trouble of going through abortion after abortion.” In China, many women whose requests for sex screening are rejected by aboveboard hospitals later arrange illegal screenings and terminate their pregnancies at unlawful clinics. My colleagues in the obstetrics department have even treated women who say they have been pregnant five or six times, yet have given birth only once and do not have a history of natural miscarriage.

Sex selection abounded in China’s ultrasound rooms and abortion clinics during the 1980s and ’90s, but laws and regulations enacted since 2001 have forbidden hospitals from carrying out the procedure. Unfortunately, this has led to the emergence of a network of so-called black clinics: underground establishments that offer illegal sex screening and abortions, and are usually operated by unqualified personnel. When preimplantation genetic diagnosis technology — a way of profiling the genes of an embryo before implantation in the womb — was first used in Chinese clinics in 1999, some of these customers then began appearing at underground IVF clinics, too.

When I explain the mechanics of IVF to a couple, some ask if they can use the technology to ensure that they have a boy.

- Yang Yang, doctor

In the vast majority of cases, couples undergo illegal sex screening because they want to give birth to a boy, not a girl. Chinese society has historically favored sons over daughters for a number of reasons, particularly the notion that only sons can continue the family line. Although this cultural preference for boys harms society as a whole, couples who opt for illegal sex screening never seem to remember that many of their hoped-for baby boys will one day struggle to find romantic partners, thanks to their parents’ contribution to the country’s skewed sex ratio.

According to data issued at the end of 2014 by China’s National Bureau of Statistics, there were nearly 34 million more men than women in the country. In many provinces — particularly in rural areas — the gender imbalance among the marriageable population has led families of brides-to-be to demand extortionate betrothal gifts worth tens of thousands of yuan. The shortage of women is probably also a factor in the rising number of scam marriages, where women marry men in order to cheat them out of their wealth before later divorcing them. A great many men of marriageable age are unable to find a spouse, leading to the emergence of “bachelor villages.” In Laoya, a village in eastern China’s Anhui province, there are more than 113 men for every 100 women — but around 60 percent of women choose to marry men from outside the village.

According to the 2009 book “The Female Deficit and the Security of Society” — written by Jiang Quanbao and Li Shuzhuo, two professors of population studies at Xi’an Jiaotong University — China’s sex ratio at birth (SRB) has frequently skewed in favor of boys since antiquity. In the 14th century, the book claims, 113 boys were born for every 100 girls. By the early 20th century, the ratio was 120 boys to 100 girls.

Between the founding of the People’s Republic of China in 1949 and the early 1980s, the country’s SRB did reportedly fall to a roughly normal level. But after the implementation of the one-child policy, it once again began to rise and may have reached as high as 121 boys for every 100 girls in 2004.

For reference, the normal SRB of a highly populated country should fall somewhere between 103 and 107 men for every 100 women, because male births are statistically slightly more likely than female births. Lying between that figure and such numbers as the 2014 SRB of 115-to-100 are the girls who have “disappeared,” either through abortion, infanticide, or nonregistration of birth. Such an imbalance between the sexes is a threat to social stability and economic growth; imperial Chinese history offers several examples of social unrest caused by a surfeit of unattached and unfulfilled men.

If we do not overhaul our overall preference for sons, then it will be impossible for us to escape China’s current population trap.

- Yang Yang, doctor

As stated above, China’s family planning law has banned sex screening since 2001. The following year, the government issued provisions to standardize medical techniques like ultrasound scans, medication used for terminating pregnancy, and equipment used in the testing of chromosomes.

But to date, tighter regulations have had a limited effect on the disappearance of China’s baby girls. It goes without saying that, even today, there are still all kinds of illegal ultrasound facilities and black clinics. And my own experiences along with those of my colleagues in obstetrics have convinced me that certain forms of malpractice may even persist in legitimate hospitals.

It is therefore difficult to be optimistic about the efficacy of the current anti-screening laws. The demand is there, but hospitals cannot satisfy it; in a society like China, where informal person-to-person relationships drive all manner of transactions, people almost always find a way to skirt the system.

Researchers tend to attribute the disappearance of Chinese girls to three causes. The first includes so-called direct factors like the tragic cases of infanticide or child abandonment that sometimes make the news. Other direct factors include indefinitely delaying the registration of an infant girl’s birth and aborting a fetus based on its sex.

The second cause comprises so-called conditional factors, referring primarily to the marked decrease in the birth rate brought about by family planning restrictions. And the third cause includes more fundamental factors like the deep-seated preference for sons in a profoundly patriarchal society.

If we do not overhaul our overall preference for sons, then it will be impossible for us to escape China’s current population trap. Today, following the end of the one-child policy and the relaxation of family planning laws to allow all couples to have two children, we can at least hope for an eventual increase in registrations of female births and a general growth in the birth rate, both of which, if allowed to function normally, will help to bring down the SRB.

As a fertility doctor, it goes without saying that I will abide by the legal and ethical constraints of my profession. But this is not enough. I also call on others to understand the simplest of principles: Having a daughter is just as beautiful, just as life-affirming, as having a son.

We must shake off our harmful social preference for boys — because no more little girls should ever disappear, and no more little boys should have to grow old alone.